There is considerable morphological evidence that neutrophils can migrate through various types of epithelium. However, it is not known if the degree of permeability of the epithelium imposes restrictions on the rate or direction of leukocyte migration. It is also unclear what effect emigrating neutrophils have on the epithelial permeability, occluding junction disassembly and reformation. To answer these questions an in vitro model system has been developed to study transepithelial migration of human neutrophils. A monolayer of kidney epithelial cells of known permeability grown on a micropore filter is used to separate neutrophils placed in the upper compartment of a modified Boyden chemotactic chamber from a chemoattractant in the lower compartment. The rate of neutrophil migration through epithelia from both the apical and basal regions of the cell will be assessed as a function of time by chemotactic assay and the morphology of this process studied by transmission and scanning electron microscopy. The degree of epithelial permeability (determined by transepithelial resistance, ultrastructural and radioactive tracer and freeze-fracture studies) on the rate of neutrophil emigration will be quantitated by chemotactic assay as a function of time. The influence of chemoattractants and temperature on this process will be investigated. The effect of emigrating neutrophils on epithelial permeability will be examined by transepithelial electrical resistance studies during neutrophil emigration and correlated with ultrastructural and radioactive tracer studies. The disassembly and reassembly of occluding junctions during neutrophil emigration will be examined at short time intervals by ultrastructural tracer, scanning and freeze-fracture electron microscopy. This project will result in an increased knowledge of structural and physiological factors involved in transepithelial migration of human neutrophils and will provide a system to study and detect impaired leukocyte emigration.